How do I create a method in django models that returns the sum of a field in that same model?

Question

I'm new to Django and I have two models set up like this currently. I want to calculate, in the Climber model, that returns the total points that climber has earned by accessing the climbs_completed field. How can I go about doing this? In other words, how do I sum up the points for each Climb in climbs_completed ? Is there a better way to do this besides writing a method? Thank you in advance!

class Climb(models.Model):
    name = models.CharField(max_length=20, default='')
    grades = [('v'+str(i),'v'+str(i))for i in range(0,13)]
    grade = models.CharField(max_length=3, choices=grades, default='v-1')
    weeks = [(i,i)for i in range(1,13)]
    week = models.IntegerField(choices=weeks, default=0)
    points = models.IntegerField(default=0)

    def __str__(self):
        return self.name

class Climber(models.Model):
    user = models.OneToOneField(User, on_delete=models.CASCADE)
    grades = [('v'+str(i),'v'+str(i))for i in range(0,13)]
    highest_grade = models.CharField(max_length=3, choices=grades, default='v0')
    team = models.ForeignKey(Team, null=True, on_delete=models.SET_NULL)
    climbs_completed = models.ManyToManyField(Climb, blank=True)

    def __str__(self):
        return self.user.username

    # for each climbs_completed, sum up the points
    def total_score(self):
        pass

Answer 1

You can use Sum and add the total climb points as annotated value like this:

from django.db.models import Sum

climbers = Climber.objects
print(climbers.values('pk', ))

Or you can use aggregation in the total_score method, like this:

class Climber(models.Model):
    ...

    def total_score(self):
       return self.climbs_completed.

First method is more efficient if you want to get values from bunch of climbers and do it in one database hit.